Control method and apparatus for heavy media separation process



Feb. 15, 1966 CONTROL METHOD AilD APPARATUS FOR HEAVY MEDIA SEPARATION PROCESS D L. NELSON Filed Jan. 5, 1961 Ala/Mal all-mes /55 Adder IO 20 R221 Preparcfr'on Ore Screen W F Sp ay lvazzleL Separa T0)" 1 l2 Bra/had f H w J/fmes I4 32 3O 34 r a g 28 36 Sink 931k F7002 F1 1: I Screen Producfg Screen producz Wafer Drain Drain I PP y W a I 44 l Densily Densify /42 I P 24 Gauge Gauge l 1 /38 I t Heavy Media P P I Circulation Sump V I D///e/en(e 46 Heavy Com Pater I Media h Supply 52 48 Recorder con frol ConIroI/er 54 Poznl c7 1 [I I] F1002 /3O 32- Sink Screen Screen Cam/4;)?!" 46 7a Ca/r/pufer 4e f IL 5:

42 f q 60 44 11 7a Densz 1y p f 2 9 DenSZ-fi-er Jump 24 Gauge epora or P k w L "M8 11 6 62 l Wnsfe 58 6| J "E 7 0 I I Sump 66 y 2 Invcnfor T 24 64 J I awe/QC 92m lSeporalor- 20 L United States Patent 3,235,072 CONTROL METHOD AND APPARATUS FOR HEAVY MEDIA SEPARATION PROCESS David L. Nelson, Minneapolis, Minn., assignor to Industrial Nucleonics Corporation, a corporation of Ohio Filed Jan. 5, 1961, Ser. No. 80,815 6 Claims. (Cl. 209-12) This invention relates generally to an ore dressing process, and more particularly to a novel method and means for controlling a heavy media separation process.

In a typical heavy media sink and float separation process, there is generally introduced a mixture of solid particles of diflerent specific gravities to be separated, such as crushed coal, ore or other mineral agglomerate, into a heavy liquid or medium. The heavy medium is of a specific gravity intermediate the specific gravities of the solid particles to be separated. Solid particles having a specific gravity less than that of the heavy medium float to the surface while solid particles having a specific gravity greater than that of the heavy medium sink in the medium. The resulting float and sink fractions of the separation are appropriately removed from the separatory apparatus, such as by drum, cone, trough or the like. Usually the heavy medium is an aqueous suspension of a finely divided solid, such as finely ground galena, barites, silica, hematite, magnetite, ferrosilicon and mixtures of one or more of these with other minerals.

In the process the medium is recovered from the sink and float products and circulated back through the separatory vessel. However, the introduction of slimes, extremcly fine particles, inevitably accompanying the ore to be separated, into the separatory vessel causes contamination of the medium. These variations in the mass flow of slimes into the separator will be reflected as changes in the gravity of the medium. In addition, the solids constituent of the medium will gradually decrease due to the incomplete recovery of the medium from the sink, float and wash screen drains. The recovery of the process is defined as the percentage of the useful product shipped divided by the total tonnage introduced to the process in the same period. The ditference comprises tailings and waste material which come over the float screens. If the gravity of the media increases, the iron concentration in the sink product increases but the actual recovery rate declines. If the gravity decreases, much of the desired ore is lost. In either case the process is not being operated in the most efficient manner possible.

Previous attempts at controlling the heavy media density have not been entirely satisfactory. Heretofore it has been necessary to periodically sample the media with a Denver cup, a mechanical beam scale more suitable for a laboratory than an industrial process. The solids concentration of the heavy media was then adjusted in accordance with the sample measurements. In general, the measurements have been too few and too time-consuming to provide operating personnel with data truly representative of the dynamic nature of the process variable. By the time corrective action can be taken, the variable may have already begun an increase in a direction opposite to that indicated by the sample measurement. In addition, due to the inaccessibility of the interior of the separatory vessel, the sample measurements have been made downstream and are not easily correlated with conditions actually existing in the separator.

To overcome these difliculties, the present invention provides apparatus for continuously measuring the density of the drain flow of both the sink screen and the float screen. The difference between these two density measurements is computed and compared with a desired value.

3,235,072 Patented Feb. 15, 1966 ice Whenever the computed differential deviates from the desired value, an error signal is derived and utilized as a .control signal. The rate at which water is admitted to the preparation screen is adjusted in accordance with the control signal to rinse more or less of the slimes from the ore to be separated. Auxiliary control loops are also provided in the heavy media recirculation and magnetic separation systems of the heavy media separation process.

Accordingly, it is a primary object of the present invention to provide an improved automatic density control system for a heavy media separation process.

In is another object of the present invention to provide a control system for a heavy media separation process which is based upon more accurate measurement of the heavy media density than heretofore available.

It is also an object of the present invention to provide a control system for a heavy media separation process which increases the desirable throughput of the process.

It is yet another object of the present invention to provide a control system for a heavy media separation process which is readily adaptable to industrial processes already in existence.

These and other objects and advantages of the present invent-ion will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of .a heavy media separation process controlled in accordance with the present invention; and

FIG. 2 is a partial diagrammatic view of the process of FIG. 1 employing additional control loops in accordance with the present invention.

With reference now to the drawings and specifically to FIG. 1, there is shown a heavy media separation process for classifying ore. Raw ore is placed on a preparation screen 19. Slimes inevitably accompanying the raw ore are rinsed therefrom by a spray nozzle 11 providing a continuous shower of water admitted to the screen 10 by a conduit 12 and an adjustable valve 14. A drain 13 serves to remove the rinsed slimes from the screen 10. A water supply generally shown at 18 may contain a reservoir and suitable pumping apparatus for maintaining pressure in the conduit 12. The rinsed ore is fed into a separator 20 which may be of the drum, cone, or trough type.

The heavy liquid media required for separation is supplied at 22 to a circulation sump 24. The source of heavy media 22 may comprise a portion of a media recovery system which is described in detail hereinafter. A pump 26 moves the heavy media into the separator 20 over a conduit 28.

The output of the separator is extracted from the float screen 30 and sink screen 32 through outlets 34 and 36 respectively. The drain from the screens comprises a mixture of heavy media, slimes and other mineral components. The drain from the float screen 30 flows through a conduit 38. The drain from the sink screen 32 flows through a conduit 40. Both of the screen drains empty into the heavy media circulation sump 24.

The quality of the sink and float products provided at outlets 34 and 36 suffers when the density of the heavy media in the separator 20 deviates even slightly from a desired value. In the practice of the present invention, the density of the float screen drain flow is measured by a gauge 42 inserted in conduit 38. The density of the sink screen drain flow is measured by a similar gauge 44 inserted in conduit 40. The density gauges 4-2, 44 are preferably of the radiation absorption type such as disclosed in a copending application for US. Letters Patent, Serial No. 19,665, filed April 4, 1960, by Ross L.

Campbell, Jr., and Edward W. Carpenter; however, any electrical, mechanical or electro-mechanical density transducer may be used. While the illustrated process is not subject to variation in temperature and pressure which would adversely affect the media density measurement, it may be advisable to install pinchvalves below each of the gauges 42, 44 to insure that the drain conduits are continuously filled with heavy media. Signals pp and p corresponding to the measured densities of the float and sink screen drains are transmitted to a difference computer 46.

Computer 46 provides an output on line 48 proportional to the difierential density existing in the separator 20. The differential density-functional signal on line 48 comprises the input to a recorder-controller 56 which is mechanically coupled as at 52 to the adjustable Water valve 14. The recorder at 50 may be preferably of the circular chart type. Controllers found by applicant to have suitable characteristics for use may be classified into two general types. One type is referred to as a continuous or integrating controller such as described in a copending application Serial No. 657,434, filed May 6, 1957, by Richard F. Warren, now patent No. 2,999,406, issued September 12, 1961. The other is a reset type controller described in US. Letters Patent No. 2,895,888, issued July 21, 1959 to Donald E. Va-rner. The controlpoint of the controller 50 inserted at 54 may comprise a signal representative of a desired value for the differential of the measured densities. In a typical process, the desired specific gravity difference value should approach 0.15. It is this value of differential density about which the controller 50 operates.

The operation of the present invention proceeds in the following manner: Assume that the differential gravity drops below 0.15. Recorder-controller 50 opens the valve 14 to increase the mass flow of water into the preparation screen 10. Additional slimes are removed from the ore and the differential gravity increases. Next, assume that the differential gravity rises above the control point value. The recorder-controller t) reverses the direction of rotation of the valve 14 thereby reducing the Water flow to the preparation screen it). The valve 14 may be provided with high and low limit switches to advise operating personnel that further corrective action such as the manual addition of slimes as at 55 may be required.

To provide improved control of the short-term variations in the float and sink products, the system of FIG. 1 may be modified by incorporating another density control loop in the media recovery section. The two control loops exercise an improved synergetic control much better than could be realized by either loop alone. Referring to FIG. 2, a portion of the screen drains are pumped as at 56 into a magnetic separator 58 having a waste outlet 59 for tailings. The remaining media is extracted and transmitted to a densifier 60 having a rake 61. The raked media product is fed to the sump 24 where it is combined with the float screen drain opportioned by a valve commonly known as a buggy 70. The density of the raked product depends on the position of the rake. Since the media is tranported at a fixed velocity v determined primarily by the pump 26, a change in density p is reflected as a change in mass flow M= vA where A is the cross-sectional area of flow.

In addition to the water valve correction the density gauge 42 initiates by means of a controller 62 control of the rake position in the densifier 60. As the rake 61 is lowered and raised the amount of rake product transmitted to the sump is respectively increased or decreased. Accordingly, to maintain the desired media density in the sump, the controller 62 lowers the rake 61 when the density of the float screen drain decreases. Similarly, the rake position is raised when an increase in drain density is detected at 42. It will be apparent that the gauges 42 and 44 continue to supply information 'to the ratio computer 46 to enable concomitant Water valve adjustments. Alternatively, it may be desirable to control the addition of water to the densifier rather than the rake position.

It has been found to be further helpful to continuously maintain a given sump level at 24. A fill height gauge 64 is utilized in conjunction with a controller 66. It has been found preferable to employ a floating control action at 66 in accordance with known techniques. The controller 66 is mechanically coupled as at 68 to an apportioning valve 70 commonly known as a buggy which rides back and forth below the float screen 30. As the sump level drops below a desired height, controller 66 moves the buggy 70 to divert more media to the sump 24. If the level increases beyond the desired height, the buggy 70 is moved in the opposite direction to divert more of the float screen drain flow through the magnetic recovery system;

The primary and secondary control loops of the present invention have been described in terms not intended to limit the invention but rather to expedite the explanation of applicants inventive concepts which are explicitly defined in the following claims.

I claim:

1. The method of controlling the operating density of a heavy media separation process in which orebearing slimes are admitted to the input of a separator also having a float screen drain and a sink screen drain recirculated thereto, comprising the steps of measuring the density of said float screen drain, measuring the density of said sink screen drain, computing the difference between said densities, and controlling the removal or addition of said slimes at said separator input in accordance with said computed difference.

2. The method of controlling the operating density of a heavy media separation process including a separator receiving ore bearing slimes at the input thereof, a sink screen and a float screen for removing a separating medium, and a recirculating sump for transferring a portion of the drains of said sink screen and said float screen directly to said separator, the remaining portion of said screen drains being transmitted to said sump from a magnetic separator system including a magnetic separator for removing metallic waste products from said remaining portion, and a densifier for adjusting the density of said remaining portion, said method comprising the steps of:

measuring the density of said float screen drain,

measuring the density of said sink screen drain, computing the difference between said measured densities,

controlling the removal or addition of said slimes at said separator input in accordance with said computed difference,

controlling the density of said remaining portion in said densifier in accordance with said measured float screen drain density,

measuring the height of said sink and float screen drains in said sump, and

adjusting said remaining portion of said float screen drain transmitted to said magnetic separator system in accordance with said measured sump level.

3. Apparatus for controlling the operating density of a heavy media separation process in which ore bearing slimes are admitted to the input of a separator also having a float screen drain and a sink screen drain recirculated thereto, comprising means for measuring the density of said float screen drain, means for measuring the density of said sink screen drain, means for computing the difference between said densities, and means for controlling the removal or addition of said slimes at said separator input in accordance with said computed difference.

4-. Apparatus for controlling the operating density of a .heavy media separation process including a separator receiving ore bearing slimes at the input thereof, a sink screen and a float screen for removing a separating me dium, and a recirculating sump for transferring a portion of the drains of said sink screen and said float screen directly to said separ-ator, the remaining portion of said screen drains being transmitted to said sump from a magnetic separator system including a magnetic separator for removing metallic waste products from said remaining portion, and a densifier for adjusting the density of said remaining portion, said apparatus comprising:

means for measuring the density of said float screen drain, means for measuring the density of said sink screen drain, means for computing the difference between said measured densities, means for controlling the removal or addition of said slimes at said separator input in accordance with said computed difierence, means for controlling the density of said remaining portion in said densifier in accordance with said measured float screen drain density, means for measuring the height of said sink and float screen drain in said sump, and

means for adjusting said remaining portion of said float screen drain transmitted to said magnetic separator system in accordance with said measured sump level.

5. Apparatus substantially as set forth in claim 4 in which said means for controlling the density of said remaining portion in said densifier comprises a rake for said densifier, and means for controlling the position of said r-ake.

6. Apparatus substantially as set forth in claim 4 in which said last named means comprises a buggy below said float screen, and means for controlling the position of said buggy relative said float screen drain.

References Cited by the Examiner UNITED STATES PATENTS 2,320,519 6/1943 Hirst 209-1725 2,877,896 3/1959 Jones 209-172.5 3,093,577 6/1963 Wilmot 209-172.5

HARRY B. THORNTON, Primary Examiner. ROBERT A. OLEARY, Examiner. 

3. APPARATUS FOR CONTROLLING THE OPERATING DENSITY OF A HEAVY MEDIA SEPARATION PROCESS IN WHICH ORE BEARING SLIMES ARE ADMITTED TO THE INPUT OF A SEPARATOR ALSO HAVING A FLOAT SCREEN DRAIN AND A SINK SCREEN DRAIN RECIRCULATED THERETO, COMPRISING MEANS FOR MEASURING THE DENSITY OF SAID FLOAT SCREEN DRAIN, MEANS FOR MEASURING THE DENSITY OF SAID SINK SCREEN DRAIN, MEANS FOR COMPUTING THE DIFFERENCE BETWEEN SAID DENSITIES, AND MEANS FOR CONTROLLING THE REMOVAL OR ADDITION OF SAID SLIMES AT SAID SEPARATOR INPUT IN ACCORDANCE WITH SAID COMPUTED DIFFERENCE. 